In the ITU-R (International Telecommunication Union Radio communication sector), a standardization work for IMT (International Mobile Telecommunication)-Advanced (i.e., the next-generation mobile communication system after the third generation) is in progress. IMT-Advanced sets its goal to support IP (Internet Protocol)-based multimedia service at the data transfer rate of 1 Gbps in stop and slow-speed moving states and of 100 Mbps in a fast-speed moving state.
One of the powerful candidates as a system standard to satisfy the requirements of IMT-Advanced is LTE-A (Long Term Evolution-Advanced) of 3GPP (3rd Generation Partnership Project). LTE-A is an improved version of 3GPP LTE (hereinafter referred to as ‘LTE’). LTE is part of E-UMTS (Evolved-UMTS) using an E-UTRAN (Evolved-Universal Terrestrial Radio Access Network). The LTE adopts OFDMA (Orthogonal Frequency Division Multiple Access) in downlink and SC-FDMA (Single Carrier-Frequency Division Multiple Access) in uplink.
In the LTE-A, consideration is taken of a relay station to be included in a wireless communication system. The relay station functions to extend the cell coverage and improve transmission performance. A base station can have an advantage of extending the cell coverage by servicing mobile stations, located in the cell coverage thereof, through relay stations. Further, since the relay stations improve transmission reliability between the base station and the mobile stations, the transmission capacity can be increased. A relay station may be utilized in the case in which a mobile station is located in a shadow region although it is within the coverage of a base station.
A relay station commonly divides subframes into a reception subframe for receiving a signal from a mobile station connected thereto and a transmission subframe for sending a signal to a base station in order to prevent self-interference. Here, guard time needs to be placed in the reception subframe or the transmission subframe of a signal. The guard time is used for stabilization and the prevention of interference according to the transmission/reception switching of a signal in a relay station. If the guard time is included in the transmission subframe, available time resources that the relay station can transmit a signal to the base station are reduced.
Meanwhile, in a wireless communication system environment, fading is generated owing to multi-path time delay. A process of restoring a transmission signal by compensating for the distortion of the signal, generated owing to an abrupt change in the environment due to fading, is called channel estimation. In general, channel estimation is performed using a reference signal (RS) known to both a receiver and a transmitter. A relay station can also transmit the reference signal to a base station.
There is a need for a signal transmission method with consideration taken of the fact that, if a relay station transmits a signal to a base station, available time resources are gradually reduced in a link between the relay station and the base station owing to the guard time.